linux-kernel - Re: [PATCH 002 of 6] Introduce rq_for_each_segment replacing rq_for_each

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Date:	Mon, 20 Aug 2007 14:46:35 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
cc:	NeilBrown <neilb@...e.de>, Satyam Sharma <satyam@...radead.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	Tejun Heo <htejun@...il.com>,
	Cell Broadband Engine OSS Development 
	<cbe-oss-dev@...abs.org>
Subject: Re: [PATCH 002 of 6] Introduce rq_for_each_segment replacing
 rq_for_each_bio


On Aug 20 2007 13:21, Geert Uytterhoeven wrote:
>> > >> >  		dev_dbg(&dev->sbd.core,
>> > >> >  			"%s:%u: bio %u: %u segs %u sectors from %lu\n",
>> > >> > -			__func__, __LINE__, i, bio_segments(bio),
>> > >> > -			bio_sectors(bio), sector);
>> > >> > -		bio_for_each_segment(bvec, bio, j) {
>> > >> > +			__func__, __LINE__, i, bio_segments(iter.bio),
>> > >> > +			bio_sectors(iter.bio),
>> > >> > +			(unsigned long)iter.bio->bi_sector);
>> > >>                         ^^^^^^^^^^^^^^^
>> > >> Superfluous cast: PS3 is 64-bit only, and casts are evil.
>> > 
>> > bi_sector is sector_t. The cast is ok, because printf will warn, and rightfully
>> > so since sector_t may just change its shape underneath. It would not be so much
>> > of a problem if printf() was not a varargs function, but it is, and hence,
>> > passing an object bigger than the format specifier can make problems.
>> 
>> Oh yeah, that's why the _cast_ _is_ needed in the first place, by the way.
>> I was mentioning why the cast itself should be (unsigned long long) otoh.
>
>On 64-bit platforms, sector_t (which is either u64 or unsigned long, depending
>on CONFIG_LBD) is unsigned long, so there's no need for a cast. Hence there's
>no compiler warning to be silenced by adding the cast.

Note actually.. I was accidentally referring to printf rather than the
actual ^^^-marked cast. Sorry for the inconvenience.


	Jan
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